Qualitative and quantitative immuno- and chemical assays have gained acceptance as important tools in the medical and food industries. These methods have been used for the diagnosis of disease conditions, detection of analytes, and for the detection of microbes, such as bacteria. These methods of diagnosis have established effectiveness, and the methods have made it easier for physicians to monitor and manage patients undergoing various forms of therapy.
Traditionally, the diagnostic assays have been performed in hospital and clinic settings, and involve the use of sophisticated and expensive equipment, that require specially trained personnel for their operation. Further, the assay results are sometimes not available for days or weeks after the samples from the patients have been obtained. The presently available diagnostic assays are thus costly, time consuming, and not convenient.
Attempts have been made to develop less costly assays. For example, a typical home self-test for detecting blood components requires the patient to prick a finger with a sterilized lancet, apply a drop of blood sample to a sample application area on the disposable strip, and then wait for the results. Assays that use other bodily fluids, such as urine essentially work in a similar manner. These devices are designed such that a typical lay person can perform the assays correctly with very little training However, these assay systems generally suffer from low accuracy or require a number of preparative steps be performed that could compromise the test results, and are thus not convenient.
U.S. Pat. No. 5,580,794 to Allen Michael describes a single use electronic assay device that assays for specific analytes in a given sample. U.S. Pat. No. 4,806,312 to Greenquist describes a multizone analytical element having detectable signal concentration zone. U.S. Pat. No. 4,627,445 to Garcia et al. describes a hand-held portable medical diagnostic system for checking measurement of blood glucose, urea nitrogen, hemoglobin, or blood components, where a disposable needle or lance probe package carries a chemical reagent strip such as blood reacting chemistry, a visual readout, and a computer system.
U.S. Pat. No. 4,197,734 to A. Rosenberg describes an apparatus that is capable of measuring the clotting time of blood. The apparatus includes a support frame, which supports a syringe containing a blood sample, and a turntable that rotates. Blood from the syringe drops onto the turntable where the clotting time is automatically and graphically depicted by a chart that is rotated on the turntable. The apparatus can also be employed to determine variations in the viscosity of blood plasma and other fluids.
U.S. Pat. No. 3,486,859 to Greiner et al. describes an apparatus that has a double arm holder with blood liquid reactant chambers that are connected to each other via a small capillary conduit. An air pump is provided for applying pressure changes to one of the chambers to effect periodic mixing of the liquids via the capillary conduit. Indicator means are included to detect the progressive restriction of the capillary conduit upon coagulation of the blood.
The methods described above have severe limitations which make them extremely challenging for home use. Some of the methods require special blood preparations and handling, making them suitable for a central clinic with well-trained staff, while others are expensive, or not accurate. Thus, there is a need for assay systems for detecting analytes that are accurate, convenient, and inexpensive.